In recent years, there has been increasing interest in improving the air environment because of the air pollution problem, the generation of various pathogenic bacteria and viruses, the increase in the number of allergy patients, and the like. In order to respond to the demand for making the indoor environment comfortable, there have been proposed removing techniques and evaluation methods of minute substances which exist in the atmosphere and which include, for example, microorganisms such as bacteria, fungi and viruses, and minute substances such as harmful chemical substances.
Conventionally, as a method for improving the air environment, there have been generally adopted various methods for removal particles in the air by using a filter. The method is configured to clean the air by physically collecting and removing the minute substances in the air.
Further, various air cleaning techniques as represented by those using radicals and ions have been attracting attention in recent years. The techniques are based on a method for eliminating the harmfulness of the minute substances floating in the air by using the effects of denaturation, decomposition, and the like. For example, as methods for performing sterilizing treatment by irradiating microorganisms with particles such as ionized ions, there has been disclosed in Patent Document 1 a positive and negative ion generation technique for cleaning the air and a sterilization method for sterilizing bacteria floating in the atmosphere by applying the technique.
In the development of a household electric appliance using such technique, a technique to measure the air environment is very important in the product development, because the design of the product, in which design the required air cleaning function, the reduction in energy consumption, and the like, are made compatible with each other, can be effected by accurately evaluating the performance of the product.
For example, as a method for detecting and quantifying how much harmful substance exist in the environment, there is disclosed in Patent Document 2 a technique relating to an apparatus and system for measuring minute substances floating in the atmosphere.
Further, it is proposed in Patent Document 3 that a quantitative evaluation of a removal effect test, which is performed by applying some actions to substances floating in a closed space, can be effectively performed by utilizing a method and apparatus for evaluating the removal of microorganisms.                Patent Document 1: Japanese Patent Laid-Open No. 2002-095731        Patent Document 2: Japanese Patent Laid-Open No. 11-14511        Patent Document 3: Japanese Patent Laid-Open No. 2004-159508        